The invention relates to an acoustic echo canceller particularly well suited for use in a hands-free terminal or teleconference system. The echo canceller is designed to assess the inherent signal attenuation occurring in the analog loop that connects the terminal to the switch mechanism of the PSTN domain or the PBX domain. The echo canceller is then adjusted in accordance with the degree of signal attenuation manifested by the loop. For high signal attenuation levels, the degree of echo control at the terminal is reduced since the signal attenuation occurring in the loop itself will compensate for the reduction, allowing to reach the echo control target at the far end of the loop (switch side). This feature avoids overly attenuating the echo at the terminal by taking advantage of the inherent echo control provided by the local loop conductors.
Legal claims defining the scope of protection, as filed with the USPTO.
1. An echo canceller for reducing a magnitude of an echo occurring in a return channel of a communication device, said communication device being coupled to a local loop connecting said communication device to a remote switch mechanism, said echo canceller including: a sensor operative to measure from the local loop at least one parameter of the local loop for assessing a degree of inherent signal attenuation manifested by the local loop, said sensor generating an output signal indicative of the degree of inherent signal attenuation manifested by the local loop; an echo attenuation device for reducing the magnitude of the echo occurring in the return channel of the communication device, said echo attenuation device being responsive to said output signal to vary a level of echo attenuation in dependence upon the degree of inherent signal attenuation of the local loop observed by said sensor.
2. An echo canceller as defined in claim 1 , wherein said echo attenuation device includes a first unit to generate an estimate of the echo and a second unit receiving said echo estimate for conditioning a signal propagating in the return channel of the communication device to inhibit echo therein.
3. An echo canceller as defined in claim 2 , wherein said first unit includes an adaptive filter.
4. An echo canceller as defined in claim 3 , wherein said adaptive filter includes an input for receiving a signal precursor of the echo occurring in the return channel of the communication device.
5. An echo canceller as defined in claim 4 , wherein said second unit is an adder to subtract from the signal propagating in the return channel of the communication device the echo estimate.
6. An echo canceller as defined in claim 2 , wherein said echo attenuation device includes a switched loss device.
7. An echo canceller as defined in claim 6 , wherein said switched loss device includes a first switched loss module for attenuating the echo signal propagating in the return channel of the communication device.
8. An echo canceller as defined in claim 7 , wherein a level of signal attenuation manifested by said first switched loss module is dependent upon the degree of inherent signal attenuation of the local loop observed by said sensor.
9. An echo canceller as defined in claim 8 , wherein said switched loss device includes a second switched loss module for processing a signal precursor of the echo in the return channel of the communication device.
10. An echo canceller as defined in claim 9 , wherein said switched loss device includes a switched loss controller to regulate a degree of signal attenuation implemented by said first and second switched loss modules.
11. An echo canceller as defined in claim 10 , wherein said switched loss controller is coupled to said sensor and includes an input for receiving said output signal indicative of a degree of inherent signal attenuation manifested by the local loop.
12. An echo canceller as defined in claim 11 , wherein said switched loss controller is operative to determine a switched loss setting of either one of said first and second switched loss modules at least partly on a basis of said output signal.
13. An echo canceller as defined in claim 1 , wherein the parameter measured by said sensor is a magnitude of electric current in the local loop.
14. An echo canceller as defined in claim 12 , wherein said first and second switched loss modules are multipliers.
15. An echo canceller as defined in claim 1 , wherein the communication device is a CPE.
16. A method for reducing a magnitude of an echo occurring in a return channel of a communication device, the communication device being coupled to a local loop connecting said communication device to a remote switch mechanism, said method including the steps of: a) measuring from the local loop at least one parameter of the local loop; b) assessing a level of inherent signal attenuation manifested by the local loop on a basis of the at least one parameter measured from the local loop; c) reducing the magnitude of the echo occurring in the return channel of the communication device at least partly on a basis of the level of inherent signal attenuation manifested by the local loop assessed at step b.
17. A method as defined in claim 16 , comprising the step of altering a degree of signal attenuation of a switched loss module in dependence of the level of inherent signal attenuation manifested by the local loop.
18. A method as defined in claim 16 , wherein the parameter measured from the local loop is a magnitude of an electric current passing in the local loop.
19. A CPE coupled to a local analog loop connecting said CPE to a remote switch mechanism, said CPE comprising: an echo canceller for reducing a magnitude of an echo occurring in a return channel of said CPE, said echo canceller including: a sensor operative to measure from the local analog loop at least one parameter of the local analog loop for assessing a degree of inherent signal attenuation manifested by the local analog loop, said sensor generating an output signal indicative of the degree of inherent signal attenuation manifested by the local analog loop; an echo attenuation device for reducing the magnitude of the echo occurring in the return channel of said CPE, said echo attenuation device being responsive to said output signal to vary a level of echo attenuation in dependence upon the degree of inherent signal attenuation of the local analog loop observed by said sensor.
20. A CPE as defined in claim 19 , wherein said echo attenuation device includes a first unit to generate an estimate of the echo and a second unit receiving said echo estimate for conditioning a signal propagating in the return channel of said CPE to inhibit echo therein.
21. A CPE as defined in claim 20 , wherein said first unit includes an adaptive filter.
22. A CPE as defined in claim 21 , wherein said adaptive filter includes an input for receiving a signal precursor of the echo occurring in the return channel of said CPE.
23. A CPE as defined in claim 22 , wherein said second unit is an adder to subtract from the signal propagating in the return channel of said CPE the echo estimate.
24. A CPE as defined in claim 21 , wherein said echo attenuation device includes a switched loss device.
25. A CPE as defined in claim 24 , wherein said switched loss device includes a first switched loss module for attenuating the echo signal propagating in the return channel of said CPE.
26. A CPE as defined in claim 25 , wherein a level of signal attenuation manifested by said first switched loss module is dependent upon the degree of inherent signal attenuation of the local loop observed by said sensor.
27. A CPE as defined in claim 26 , wherein said switched loss device includes a second switched loss module for processing a signal precursor of the echo in the return channel of said CPE.
28. A CPE as defined in claim 27 , wherein said switched loss device includes a switched loss controller to regulate a degree of signal attenuation implemented by said first and second switched loss modules.
29. A CPE as defined in claim 28 , wherein said switched loss controller is coupled to said sensor and includes an input for receiving said output signal indicative of a degree of inherent signal attenuation manifested by the local loop.
30. A CPE as defined in claim 29 , wherein said switched loss controller is operative to determine a switched loss set point of either one of said first and second switched loss modules at least in part on a basis of said output signal.
31. A CPE as defined in claim 19 , wherein the parameter measured by said sensor is a magnitude of electric current in the local loop.
32. A CPE as defined in claim 30 , wherein said first and second switched loss modules are multipliers.
33. A CPE as defined in claim 19 , wherein said CPE is a hands-free CPE.
34. An echo canceller for reducing a magnitude of an echo occurring in a return channel of a communication device, said communication device being coupled to a local loop connecting said communication device to a remote switch mechanism, said echo canceller including: sensor means operative to measure from the local loop at least one parameter of the local loop for assessing a degree of inherent signal attenuation manifested by the local loop, said sensor means generating an output signal indicative of the degree of inherent signal attenuation manifested by the local loop; echo attenuation means for reducing the magnitude of the echo occurring in the return channel of the communication device, said echo attenuation means being responsive to said output signal to vary a level of echo attenuation in dependence upon the degree of inherent signal attenuation of the local loop observed by said sensor means.
Cooperative Patent Classification codes for this invention. Click any code to explore related patents in that topic.
April 30, 1998
June 18, 2002
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